Finding the slot

14 handicapper here. My question is around finding the slot. I find that when I take one handed swings with my right arm the club drops right into the slot bisecting my right bicep on the downswing. As soon as I put 2 hands on the club and swing the shaft no longer will bisect my bicep in the downswing and I now swing over my shoulder on the downswing (ott) or steep. Why is this and how can I shallow it out so it drops in the slot like 1 handed swings?